This invention relates to radio-frequency (RF) excited gas lasers, especially to diffusion-cooled low and medium power CO2 lasers.
Prior art RF excited gas laser design pioneered by Katherine D. Laakmann (U.S. Pat. No. 4,169,251) defines an elongated laser resonator chamber being excited by transversely applied radio frequency (RF) field. This basic design of RF excited laser has been further advanced by Peter Laakmann (U.S. Pat. No. 4,805,182) through all-metal laser tube arrangement having metal electrodes and metal side-walls forming an elongated laser resonator chamber with electrodes and side-walls being diffusion-cooled by closely spaced walls of the metal tube envelope. No additional cooling of the electrodes (e.g. by liquid flowing through the electrodes) is required, which is a great advantage of this design. A disadvantage of this design is due to complexity of laser tube assembly and numerous components needed to build such a tube.
Another prior art laser design (Kruger et. al., U.S. Pat. No. 5,224,117) uses microwave excited, diffusion cooled, ridge waveguide electrode structure, which can be directly cooled through the ridge electrodes. This laser does not require additional elements such as an electrode support structure, resonant inductor coils, etc. A disadvantage of this design is that it is not applicable to 30-300 MHz excitation frequency range, which is the most effective and practical for CO2 laser excitation (Vitruk, Hall and Baker, IEEE J Quantum Electron., 30, 1623 (1994)).
Another prior art laser (P. Vitruk, pending U.S. patent application Ser. No. 09/397,434) is based on truncated ridge waveguide tube concept with resonant frequencies in 30-300 MHz band and having two ridge electrode design. Truncating the ridge significantly increases ridge structure inductance, which together with high capacitance of large area slabs electrodes allows reducing the ridge waveguide resonant frequencies from GHz band down to 30-300 MHz VHF band. This design is the most suited for high power slab laser operations requiring liquid cooling of discharge electrodes. However, commercial low power lasers do not benefit from this two ridge design since these lasers cannot use liquid coolingxe2x80x94it is extremely cost prohibiting for laser manufacturing and for later stage system level integration. A different cooling mechanism is needed for such low cost and low power lasers. Furthermore, small discharge electrode area in a low power laser leads to low inter-electrode (or inter-ridge) capacitance, which would cause an unacceptably high ridge waveguide resonant frequency and which is another disadvantage of ridge waveguide laser tube design when applied to low power RF excited lasers.
It is an object of the present invention to reduce the cost and to simplify the electrode support structure design used in gas lasers with RF excitation in 30-300 MHz band, which is the best suited for sealed CO2 laser excitation. It is a further object of the current invention to improve and simplify the cooling of electrode structure.
Truncated ridge waveguide for all-metal gas laser excitation according to present invention consists of a metal tube and a pair of endplates forming a vacuum envelope for containing a laser gas, a laser resonator mirrors placed on the endplates at the opposite ends of the tube and at least one elongated metal ridge electrode located within and conductively connected to the metal tube by at least one metal post to define a truncated ridge waveguide. The tube and the ridge electrode are shaped and positioned so as to define at least one elongated laser bore channel and a low thermal resistance and high capacitance ridge-to-tube gap therebetween. The ridge electrode and metal posts form truncated ridge to increase the ridge waveguide structure inductance, which together with high capacitance of the electrode-to-tube gap decreases the resonant frequency from the microwave band into the VHF band (30-300 MHz), which is the most suitable for CO2 laser excitation. Present invention is characterized by lower cost, simpler tube and electrode design and more efficient RF discharge plasma cooling by the inner wall of the metal tube acting as one of the discharge electrodes, and by a ridge acting as a second discharge electrode.